1. Field of the Invention
The invention concerns a method for the quantitative analysis of sample liquids by irradiating a sample that has been essentially freed of solvent and detecting the radiation that is diffusely reflected from the sample and sample carrier. In addition the invention includes a system for the analysis of sample liquids with which samples that have been essentially freed of solvent that are located on a sample carrier are irradiated and the radiation emitted from the sample is detected with a detection device. The invention additionally encompasses a sample carrier for use in a system according to the invention in which a diffusely reflecting metal layer is present on a carrier.
2. Description of the Prior Art
Methods for the qualitative analysis of sample liquids are known in the state of the art in which solids, thin layer chromatograms or residues of drying are illuminated with infrared radiation and the reflected radiation is analysed in order to obtain information on substances in the sample. In the disclosure DE-A-42 33 321 a microanalytical method is described in which the sample liquid is applied onto a plastic carrier and subsequently dried up. Measures are described in this disclosure which are aimed to achieve a layer thickness that is as large as possible and as flat a structure as possible of the residue of drying. Only part of the residue of drying is irradiated with infrared radiation using the described system and the specularly reflected radiation is analysed. Since the radiation passes through only part of the residue of drying, a quantitative analysis is only possible when exactly defined dimensions of the residue of drying can be guaranteed which in practice is very time-consuming.
In addition methods for the analysis of liquids are described in the state of the art in which for example fruit juices are applied to a glass fibre fleece and analysed by detection of reflected infrared radiation. In this case the radiation only penetrates the upper layer of the fleece. The method has to be empirically calibrated for a quantitative evaluation and is susceptible to error since a variable microstructure of the glass fibre fleece causes interference. Also in the case of the analysis of thin layer chromatograms with scanners, the radiation penetrates a not exactly defined part of the sample and therefore necessitates an empirical calibration.
The Patent Application WO 90/15981 concerns the drying of filter materials onto which sample liquids have been applied. The drying process represents a central problem in this application because an uncontrolled migration of sample constituents occurs during the drying which has an adverse effect on the homogeneity of the residue of drying. In the analytical method described in WO 90/15981 the radiation penetrates only part of the sample and is thus less suitable for a quantitative trace analysis.
The state of the art has the disadvantage that a quantitative analysis of sample liquids by measurement of the IR radiation reflected from the sample is only possible when complicated measures are carried out during the sample preparation. In particular it is not possible using the methods known in the state of the art to adequately carry out quantitative analyses when mixtures of substances are present.